The power consumption of motors has been increased in homes, industries, and transportation systems, for example, and reducing such a power consumption of motors is important considering the recent energy-saving-oriented society and the continuous increase of electric energy availability. For optimizing the energy for use in a motor, the motor is controlled in terms of output rotation speed using an AC-to-AC power conversion apparatus. The issue here is that, however, such a power conversion apparatus for use with a motor is hardly popular in the current market, and is expected to be more popular and widely used from this time forward. In order to encourage the use of the power conversion apparatus, there needs to achieve reduction of material by increasing the power density in the power conversion apparatus, and there also needs to implement a general-purpose power integrated circuit by designing the power conversion apparatus with a highly integrated design.
FIGS. 1 to 3 are each a circuit diagram of a conventional power conversion apparatus that performs power conversion into an AC load from an AC power supply via a DC section. Specifically, FIG. 1 shows an apparatus that performs power conversion into a three-phase AC load from a three-phase AC power supply via a three-phase full-bridge circuit 1, a DC link capacitor 2, and a three-phase full-bridge circuit 3. FIG. 2 shows an apparatus that performs power conversion into a three-phase AC load from a single-phase AC power supply via a single-phase full-bridge circuit 4, the DC link capacitor 2, and a three-phase full-bridge circuit 5. FIG. 3 shows an apparatus that performs power conversion into a three-phase AC load from a single-phase AC power supply via a single-phase full-bridge circuit 6, a composite chopper circuit 7, the DC link capacitor 2, and a three-phase full-bridge circuit 8.
FIGS. 4 to 7 are each a circuit diagram of a conventional power conversion apparatus that performs power conversion into an AC load from an AC power supply not via a DC section but directly. Specifically, FIG. 4 shows a direct power conversion apparatus of an indirect type, i.e., indirect matrix converter, that performs power conversion into a three-phase AC load from a three-phase AC power supply via two three-phase full-bridge circuits 9 and 10. FIG. 5 shows another direct power conversion apparatus of an indirect type, i.e., indirect matrix converter, that performs power conversion into a three-phase AC load from a single-phase AC power supply via a single-phase full-bridge circuit 12 and a three-phase full-bridge circuit 13. FIG. 6 shows an apparatus that performs power conversion into a three-phase AC load from a three-phase AC power supply via a direct power conversion circuit of a direct type, i.e., direct matrix converter, 14. FIG. 7 shows an apparatus that performs power conversion into a three-phase AC load from a single-phase AC power supply via a direct power conversion circuit of a direct type, i.e., direct matrix converter, 15.
FIGS. 8 to 13 each show a bidirectional switch for use in the power conversion apparatus described above for direct conversion from AC to AC. Specifically, FIG. 8 shows a bidirectional switch configured by a thyristor or a Gate Turn-Off thyristor (GTO) connected in reverse parallel with another. FIG. 9 shows a bidirectional switch configured by a diode bridge circuit connected with an Insulated Gate Bipolar Transistor (IGBT). FIG. 10 shows a bidirectional switch including an IGBT connected in reverse parallel with a diode, and the connecting structure is connected with another to face each other with the emitter side in shared use. FIG. 11 shows a bidirectional switch including an IGBT connected in reverse parallel with a diode, and the connecting structure is connected with another to face each other with the collector side in shared use. FIG. 12 shows a bidirectional switch including an IGBT connected in series with a diode, and the connecting structure is connected in reverse parallel with another. In FIG. 12 example, alternatively, the drift layer of the diode connected in series with the IGBT may be shared for use with another, and the resulting element piece, i.e., the reverse-blocking IGBT, may be connected in reverse parallel with another. FIG. 13 shows a bidirectional switch including a MOSFET connected with another to face each other with the source side in shared use.
In all the bidirectional switches of FIGS. 8 to 13, when any of a gate power supply, a control power supply, and a gate circuit is not activated, current flow is cut off bidirectionally.
The power conversion apparatuses of FIGS. 1 to 7 are each used as a power supply mainly for driving a motor. When the motor is driven thereby, the flow of power is directed in two directions, i.e., one is from the power supply to the motor (powering operation), and the other is from the motor to the power supply (regenerative operation). When such a flow of power is abruptly changed, the need arises to process the power of delay caused by controlling and switching inside of the power conversion apparatus. In consideration thereof, the apparatuses of FIGS. 1 to 3 are each provided with the DC link capacitor 2 of a large capacity for power processing, and the apparatuses of FIGS. 4 to 7 are each connected with a diode clamping circuit 11 for power processing.
FIG. 14 shows a specific example of the diode clamping circuit 11 for power conversion into a three-phase AC load from a three-phase AC power supply. FIG. 15 shows a specific example of the diode clamping circuit 11 for power conversion into a three-phase AC load from a single-phase AC power supply. In the diode clamping circuit, a capacitor 16 is used. The power from the load or the power supply is stored in the capacitor 16, and is discharged, as power loss, by a resistor 17 connected in parallel to the capacitor 16.
The power conversion apparatuses of FIGS. 4 to 7 have been implemented by using a semiconductor device with which the bidirectional current flow is allowed. With a conventional bidirectional switch typified by those of FIGS. 8 to 13, however, the flow of current cannot be controlled when a power failure occurs in the gate power supply, the control power supply, and the gate circuit. When the components in the power conversion apparatus, i.e., an input power supply, the gate power supply, the control power supply, and the gate circuit, suffer from sudden failures, momentary (short-time) power failures, and momentary voltage drop, or when a motor is with hard braking or is operated under light load, a diode clamping circuit is connected, and the DC link thereof is connected with a large-capacity capacitor and a discharge resistor, for processing the energy stored in the motor.
The problem here is that the DC link capacitor and the diode clamping circuit described above each occupy a large portion of volume of the power conversion apparatus, and this is the obstacle to achieve the high power density and highly integrated design of the power conversion apparatus.